Method of using sulfur-based corrosion inhibitors for galvanized metal surfaces

ABSTRACT

A composition and method for inhibiting white rust formation on galvanized surfaces. The composition includes thiols, polymeric dithiocarbamates, and xanthates. The composition may be introduced onto the galvanized surface, especially in an industrial water system, using a variety of different methods or programs including integrating with current programs or developing a new program.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 11/612,702entitled “FUNCTIONALIZED AMINE-BASED CORROSION INHIBITORS FOR GALVANIZEDMETAL SURFACES AND METHOD OF USING SAME,” filed Dec. 19, 2006, nowpending.

TECHNICAL FIELD

This invention relates generally to inhibiting corrosion on galvanizedmetal surfaces. More specifically, the invention relates to a method forinhibiting white rust corrosion on galvanized surfaces. The inventionhas particular relevance for inhibiting white rust corrosion by usingsulfide-based compounds on galvanized metal surfaces in industrial watersystems.

BACKGROUND

Galvanization is a protective zinc coating that is chemically bonded toa metal (usually iron or steel) surface. Zinc coating is used in avariety of applications and offers a certain degree of corrosionprotection for the underlying metal by providing a mechanical barrier tothe elements and environment as well as electrochemical resistance tocorrosion. Several galvanizing methods exist, such as electroplating,continuous galvanization, and hot-dip galvanization. Many industrialwater systems, such as cooling water circulation systems (sometimesreferred to herein as “cooling towers”), have such galvanized surfaces.

A common problem with galvanized coatings of all kinds is “white rust,”which manifests itself as a white, waxy, fluffy, or powderynon-protective and porous deposit that rapidly forms on galvanizedsurfaces when the surface is exposed to humid and/or wet conditions.White rust can cause considerable damage to the zinc coating and is alsodetrimental to the coating's appearance. If left unchecked, white rustwill continually corrode affected galvanized surfaces and eventuallylead to early failure of the coating. With such a non-protective, porousdeposit on the galvanized surface, the surface is not “passive” tofuture white rust formation and may rapidly continue to corrode.

Increased popularity of high alkalinity, no pH control water treatmentprograms have resulted in more frequent and severe white rust corrosionissues, especially in cooling tower applications. White rust typicallyforms if a new cooling tower is operated with water at a pH greater than8.0 for an extended period before a “basic zinc carbonate” protectivebarrier forms. To ensure long service life, the galvanized surfaces incooling towers typically must be allowed to “passivate” or form aprotective barrier prior to initial operation or start-up. Proper watertreatment and start-up procedures are also essential. One way topassivate the surfaces is to allow the zinc coating to develop a naturalnonporous surface of basic zinc carbonate during initial start-up of thecooling tower. This natural chemical barrier helps prevent or slowfurther rapid corrosion of the zinc coating from the environment as wellas from normal cooling tower operation.

This basic zinc carbonate barrier, believed to be a zinc carbonate/zinchydroxide compound (as discussed in “Guidelines for Treatment ofGalvanized Cooling Towers to Prevent White Rust,” published by theCooling Tower Institute in June 1994) typically forms within eight weeksof initial cooling tower operation with water of neutral pH (i.e., pH6.5 to 8.0) and moderately hard water environment. A typical solutecontent range would be calcium (CaCO₃) content of 100 ppm to 300 ppm asbicarbonate alkalinity and about 100 ppm CaCO₃ hardness. Formation ofthe protective zinc carbonate barrier is important for the cooling towerto resist further corrosion. Barrier absence could result in severewhite rust formation and have a significant negative impact on thecooling tower's service life.

White rust is also a form of zinc carbonate that has a different porousstructure, rate of formation, and density than the protective zinccarbonate barrier described above. If the water hardness levels,measured by CaCO₃ hardness, reach levels below 50 ppm (i.e., softwater), accelerated zinc corrosion generally results. Certain ioniccontent in the water, such as sulfates, chlorides, and nitrates atlevels greater than about 250 ppm may also contribute to acceleratedzinc corrosion. Thus, routine inspection of the cooling tower coupledwith adequate control of the water chemistry aids in the prevention ofwhite rust formation.

Current white rust corrosion prevention programs include a combinationof pre-passivating the cooling tower combined with ongoing waterchemistry management to support the viability of the passivation layer.In addition to the basic zinc carbonate protective layers, as describedabove, white rust preventatives include pretreatment with inorganicphosphate and chromate passivation. Such inorganic solutions havelimited effectiveness and are steadfastly becoming the object of federaland local regulations due to environmental concerns.

Other solutions for white rust prevention include using selectivethiocarbamates, organo-phosphorous compounds, and tannins to passivatethe surface. For example, U.S. Pat. No. 5,407,597 provides a formulationincluding a mixture of an organophosphorous compound, a thiocarbamatecompound, and soluble metal salt compound. The components of thisformulation are used as a combination and the ingredients tested alonetypically do not control white rust formation. The formulation in U.S.Pat. No. 6,468,470 B1 includes a multi-component system of anorganophosphorous compound, a tannin compound, and a soluble salt of ametal.

Moreover, under normal operating conditions, cooling towers havesubstantial evaporative water loss. As a result, large quantities of“make-up” water are introduced into the system that commonly containsionic species, such as calcium, magnesium, sulphate, and chloride.Increased alkalinity (e.g., carbonate, bicarbonate, and hydroxide ions)may also cause white rust corrosion. Particularly, accumulation ofcarbonate alkalinity, with a concomitant pH increase, creates an idealwhite rust-forming environment. This accumulation is one of the majorcauses of white rust. The presence of excess anions and/or soft watercan aggravate the degree of white rust formation by, for example,reacting with the zinc coating to produce zinc hydroxide.

As an integral component of cooling water circulation systems biocidesare essential is preventing algal, bacterial, and fungal contaminationof the systems. Some of these biocides sometimes promote white rustformation as a byproduct because they chemically react with certainwhite rust inhibitors and/or with the zinc coating. For example, sodiumhypochlorite (i.e., bleach) is a common biocide and is highly reactive.

Because high pH levels are also contributing factor to white rustformation, the addition of a sufficient quantity of free acid, commonlysulfuric acid, to the cooling water helps preclude the formation ofwhite rust. Such free acid addition creates concerns for those handlingthe free acid and also creates potential for metal corrosion from theacid itself due to overfeed or spillage. None of these passivation ormaintenance procedures described above provides a complete solution tothe white rust problem. There thus exists a need to provide efficientand improved compositions and methods of inhibiting white rustcorrosion.

SUMMARY

Accordingly, this invention provides a method of preventing corrosion ongalvanized metal surfaces. The method includes introducing an effectiveamount of a corrosion-inhibiting composition having a sulfur-based,preferably sulfide-based, white rust corrosion-inhibiting compound ontoa galvanized metal surface to form a barrier on the surface. In oneembodiment, the method further includes overlaying the barrier byreintroducing an effective amount of the composition onto the galvanizedmetal surface after one or more time intervals.

In an embodiment, the invention provides a method of inhibitingcorrosion in an industrial water system that is at least partially fullof water and has one or more galvanized metal surfaces. The methodincludes adjusting the water in the industrial water system to have a pHfrom about 6.5 to about 8.2 and introducing an effective amount of acorrosion-inhibiting composition that includes one or more sulfur-basedor sulfide-based white rust corrosion-inhibiting compounds into thewater of the industrial water system.

Implementing the method may be accomplished when the system is eitherunder load or not under load. If the system is not under load whenintroducing the corrosion-inhibiting composition, the water in thesystem is circulated after such introduction for a time interval tocontact the sulfur-based white rust corrosion-inhibiting compound withthe galvanized metal surfaces of the system to form the barrier on thosesurfaces. After a sufficient interval, the unloaded system may be turnedon or brought under load at any suitable time. If the system is underload when introducing the corrosion-inhibiting composition, the systemis operated under load after such introduction for a time interval tocontact the white rust corrosion-inhibiting compound with the galvanizedmetal surfaces of the system and form the barrier on those surfaces.

In an aspect, the invention provides a method for overlaying the barrierformed by the sulfide-based white rust-inhibiting compound. This aspectincludes overlaying the barrier while the system is under load or notunder load. If the barrier is overlaid while the system is under load,the method includes readjusting the pH of the system to be from about6.5 to about 8.2 and reintroducing an effective amount of thecorrosion-inhibiting composition into the water of the system. Thesystem is then operated under load for one or more additional timeintervals and the barrier optionally is re-overlaid after one or more ofthe additional time intervals.

If the barrier is overlaid while the system is not under load, themethod includes readjusting the pH of the system to be from about 6.5 toabout 8.2, reintroducing an effective amount of the corrosion-inhibitingcomposition into the water of the system, and circulating the water ofthe system for a sufficient interval to contact the sulfide-basedcompound with the surfaces. After the sufficient interval, the unloadedsystem may be turned on or brought under load at any suitable time.

Though the invention is particularly relevant to applications such asbasins and heat transfer coils of cooling towers, it should beappreciated that the implementation of the method is not limited to suchcooling tower applications. Contemplated applications include any systemhaving galvanized metal surfaces. The invention may also be combinedwith one or more other corrosion or scale inhibiting compositions, suchas silicates, borates, molybdates, tungstates, chromate, zinc salts,orthophosphates, polyphosphates, phosphonate/phosphinate, combinationsthereof, or any other suitable corrosion or scale inhibiting compound orcomposition, with or without one or more fluorescent tracer compounds.Such combinations would form a comprehensive corrosion and scaleinhibition program, discussed in more detail below.

An advantage of the invention is to provide a method of inhibitingcorrosion, especially white rust corrosion, on galvanized metalsurfaces.

Another advantage of the invention is to extend the lifespan ofgalvanized metal surfaces in various applications including industrialwater systems.

Yet another advantage of the invention is to provide a one-steppassivation method for inhibiting white rust corrosion on galvanizedsurfaces of industrial water systems.

An additional advantage of the invention is to provide a method forinitially pre-passivating with a sulfur-based white rustcorrosion-inhibiting composition and post-treating by overlaying thesulfur-based white rust corrosion-inhibiting composition on galvanizedsurfaces.

It is another advantage of the invention to provide an approach toinhibiting white rust corrosion on galvanized surfaces in industrialwater systems that is effective under a range of pH conditions.

It is a further advantage of the invention to provide an approach toinhibiting white rust corrosion on galvanized surfaces in industrialwater systems that is effective with water having low ionic content,such as soft water.

It is yet another advantage of the invention to provide a method forinhibiting white rust corrosion on galvanized surfaces in industrialwater systems that is effective under elevated carbonate alkalinity.

It is still another advantage of the invention to provide a compositionand method for inhibiting white rust corrosion on galvanized surfaces inindustrial water systems, which includes one or more sulfur-based orsulfide-based compounds that adsorb and/or bind to the surfaces andwhich are effective under a range of pH conditions, a range ofalkalinity levels, and a range of water hardness levels.

DETAILED DESCRIPTION

The invention provides a method of inhibiting corrosion on a galvanizedmetal surface. The method includes introducing an effective amount of acorrosion-inhibiting composition onto the galvanized metal surface toform a barrier on the surface. The term “barrier” as used hereinincludes surface modification of the galvanized surface, change ofmorphology of the galvanized surface, chemical interaction of any of thewhite rust corrosion-inhibiting compounds with the galvanized surface,or any other similar modification of or interaction with the surface. Inone embodiment, an effective amount of the corrosion-inhibitingcomposition includes from about 0.001 weight percent to about 100 weightpercent of the white rust corrosion-inhibiting compound. In a preferredembodiment, an effective amount of the composition includes from about0.001 weight percent to about 50 weight percent of the compound. In amore preferred embodiment, from about 0.1 weight percent of to about 30weight percent of the compound of the composition is introduced to thegalvanized surface.

It should be appreciated that the white rust-inhibiting compoundsdescribed herein can each be used independently, simultaneously,sequentially, alternating between different compounds, or byimplementing in any suitable order or fashion. Representativesulfur-based white rust-inhibiting compounds include thiols,bismuthiols, dimerized bismuthiols, polymeric dithiocarbamates,xanthates, and combinations thereof.

In one aspect, introducing the corrosion-inhibiting composition onto thegalvanized surface includes incorporating the method into a hot dipmanufacturing process. For example, the metal would first be dipped inmelted zinc at 450° C. (temperature at which iron/steel and zinc sharegreat affinity) where the metal would be protected with a zinc coating.The next step in the manufacturing process would be to dip thezinc-coated metal into the corrosion-inhibiting composition includingthe sulfur-based or sulfide-based white rust corrosion-inhibitingcompound.

In another aspect, such introduction includes spraying a solution of thecorrosion-inhibiting composition directly onto the surface, includingsurfaces in industrial water systems. In one embodiment, the compositionis mixed with a foaming agent to form a mixture and the mixture issubsequently sprayed onto the galvanized metal surface using anysuitable spraying device. Foaming agents may include surfactants, suchas alkoxylated alcohols, polyethylene glycol, or any other suitablesurfactant. In alternative embodiments, the composition may bephysically applied onto the surface by rolling using a paint roller orthe like, brushing using a paintbrush or the like, swabbing using a mopor the like, or by using any other suitable method or technique.

In another aspect, the corrosion-inhibiting composition is reintroducedonto the surface one or more times after one or more time intervals to“overlay” the barrier or “re-passivate” the surface. Ongoing overlayingsteps to renew the corrosion-inhibitory barrier and/or to re-passivatethe galvanized surfaces are also contemplated. As determined on acase-by-case basis, the method may include a plurality of differentcorrosion-inhibiting compositions and overlaying the barrier may includeintroducing a different one or more of the corrosion-inhibitingcompositions onto the galvanized metal surface(s).

In one embodiment, an effective amount of the corrosion-inhibitingcomposition is introduced into the water of a cooling water circulationsystem (sometimes referred to herein as “cooling tower”) to form abarrier on (or passivate) any galvanized metal surfaces of the system.It should be appreciated that such introduction may be into a new,unused system prior to initial operation of the system or into arunning, operational system. The corrosion-inhibiting composition of theinvention may be introduced into any industrial water system as eitheran adjunct treatment in combination with other compositions or programs,such as scale and/or corrosion-inhibiting programs, or as a stand-alonetreatment program, as described in more detail herein.

The industrial water system is at least partially full of water and hasone or more galvanized metal surfaces. The method includes adjusting thewater in the system to have a pH from about 6.5 to about 8.2. In apreferred embodiment, the pH of the water in the system is adjusted tobe from about 6.8 to about 7.8. The method further includes introducingan effective amount of a corrosion-inhibiting composition that includesone or more white rust corrosion-inhibiting compounds into the water ofthe industrial water system.

The corrosion-inhibiting composition typically includes from about 1 ppmto about 10,000 ppm of the white rust corrosion-inhibiting compound. Ina preferred embodiment, the composition includes from about 1 ppm toabout 1000 ppm of the compound. In a more preferred embodiment, thecomposition includes from about 1 ppm to about 100 ppm of the compound.

In one embodiment, an effective amount of the corrosion-inhibitingcomposition is introduced into the water of the industrial water systemwhen the system is operating and under load. In this embodiment, duringand after introducing the composition into the system, the system isoperated under load (i.e., turned on) for a time interval to contact thewhite rust corrosion-inhibiting compound with the galvanized surface(s)in the system to form a barrier on the surface(s).

Certain cases may require overlaying the barrier. Such overlaying may beimplemented when the industrial water system is operating and under loador when the system has been turned off and thus not under load. In oneembodiment, overlaying the barrier includes unloading (i.e., turningoff) the system, readjusting the pH of the system, reintroducing aneffective amount of the corrosion-inhibiting composition into the waterof the system, and circulating the water of the system. In anotherembodiment, overlaying the barrier includes keeping the system underload, readjusting the pH of the system (as described above) andreintroducing an effective amount of the corrosion-inhibitingcomposition into the water of the system.

In an embodiment, the method includes a plurality of differentcorrosion-inhibiting compositions and overlaying the barrier includesintroducing a different one or more of the corrosion-inhibitingcompositions into the industrial water system.

It should be appreciated that the corrosion-inhibiting composition ofthe invention is preferably introduced in a pre-passivation processprior to initially starting up the industrial water system. This methodis preferred because such application typically provides the highestdegree of passivation and protection for the galvanized surfaces in thesystem. Alternatively, the corrosion-inhibiting composition may beintroduced to a currently operating or running system. As describedabove, such an application may be implemented without turning off thesystem by leaving the system under load during the passivation processor by turning off and unloading the system.

Although not required to implement this invention, it is contemplatedthat the corrosion-inhibiting composition may be combined with one ormore other corrosion inhibitors, one or more scale inhibitors, one ormore fluorescent tracers, one or more water treatment polymers, one ormore polyalkoxy compounds, or any other suitable adjunct or additionalcomponent. Any such adjuncts may be part of an existingcorrosion-inhibitive program to which the invention becomes anadditional component or program. Adjuncts may be part of thecorrosion-inhibiting composition or may be another separate compositionor compositions. In alternative embodiments, such adjuncts may be addedsimultaneously or sequentially with the corrosion-inhibiting compositionof the invention.

Exemplary other corrosion and scale inhibitors include tungstate;molybdate; vanadate; phosphate; phosphonate; phosphinate; silicate;borate; zinc and its salts; polycarboxylates; benzoic acid; the like;combinations thereof, or any other suitable corrosion or scaleinhibitors. Exemplary water treatment polymers include polyacrylic acid;polymaleic acid; copolymers and terpolymers of acrylic acid, mateicacid, acrylamide, and acrylamidopropyl sulfonate; prism polymers;sulfonate-based polymers; and terpolymers or copolymers of acrylic acid,acrylamide, sulfomethylated acrylamide, the like, and combinationsthereof.

EXAMPLES

The foregoing may be better understood by reference to the followingexamples, which are intended to be illustrative and are not intended tolimit the scope of the invention.

Example I

Galvanized mild steel metal coupons were tested based on weight afterexposure to “Standard 13” make-up water (Ca: 440 ppm (CaCO₃); Mg: 220ppm (CaCO₃); M-alkalinity: 340 ppm; Cl⁻: 312 ppm (CaCO₃); (SO₄)²⁻: 211ppm (CaCO₃); pH controlled using NaHCO₃/Na₂CO₃ buffer at pH 8.9).Controls and samples included a phosphonate-based scale inhibitorprogram. The Controls had no additional corrosion inhibitor. BothSamples 1 and 2 included about 10 ppm bismuthiol. Corrosion rates werebased on coupon weight after 7 days of exposure and measured in mils peryear (“mpy”), as shown in Table I.

TABLE I Treatment mpy Control - A 11.7 Control - B 8.4 Sample - A 2.7Sample - B 1.5

Example II

Linear polarization electrochemical experiments were performed in a 10liter cell using galvanized metal surfaces of hot-dipped galvanized(“HDG”) rotating electrodes (H-controlled at pH 7.5). The control andsample included a passivation step with 100 ppm of a phosphonate,phosphate, and polymer-based multi-functional water treatment program.The following synthetic water chemistry including calcium chloridedihydrate, magnesium sulfate heptahydrate, and sodium bicarbonate (basedon calculated values) was used: Ca²⁺: 150 to 170 ppm (as CaCO₃); Mg²⁺:75 to 85 ppm (as CaCO₃); M-Alkalinity: 85 to 105 ppm (as CaCO₃); Cl⁻:105 to 120 ppm (as Cl⁻); and (SO₄)²⁻: 72 to 82 ppm (as (SO₄)²⁻). Thecontrol and sample also included a second step, where the passivatedelectrodes were exposed to a more extreme corrosive environment, as inExample I above. Initial corrosion rate (from 0 to 24 hours) followed bya longer duration corrosion rate (24 to 72 hours) were measured in mpy.Table II describes the initial and longer duration corrosion rates.

TABLE II Treatment 0 to 24 hour mpy 24 to 72 hour mpy Control 3 to 8 3to 4 No white rust inhibitor Post-treatment with 100 ppm treatmentprogram as above Sample ~0.5 to ~0.9 ~0.3 to 0.5   Post-treatment in 100ppm treatment program as above combined with 10 ppm white rust inhibitor(bismuthiol)

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the invention and withoutdiminishing its intended advantages. It is therefore intended that suchchanges and modifications be covered by the appended claims.

1. A method of inhibiting corrosion on a galvanized metal surface, saidmethod comprising: (a) introducing an effective amount of acorrosion-inhibiting composition onto the galvanized metal surface toform a barrier on said surface, said composition including asulfide-based white rust corrosion-inhibiting compound; and (b) afterone or more time intervals, optionally overlaying the barrier byreintroducing an effective amount of the composition onto the galvanizedmetal surface.
 2. The method of claim 1, wherein the sulfide-based whiterust corrosion-inhibiting compound is selected from the group consistingof: thiols; bismuthiols; dimerized bismuthiols; polymericdithiocarbamates; xanthates; and combinations thereof.
 3. The method ofclaim 1, wherein the galvanized metal surface is part of an industrialwater system.
 4. The method of claim 1, including preparing a solutionof the corrosion-inhibiting composition including from about 0.001weight percent to about 100 weight percent of the sulfide-based whiterust corrosion-inhibiting compound.
 5. The method of claim 1, includingspraying or physically applying an effective amount of said compositiondirectly onto the galvanized metal surface.
 6. The method of claim 1,including dipping the galvanized metal surface into a solutioncontaining the corrosion-inhibiting composition.
 7. The method of claim1, including mixing a foaming agent with the corrosion-inhibitingcomposition to form a mixture and spraying an effective amount of themixture onto the galvanized metal surface to form the barrier.
 8. Themethod of claim 1, including a plurality of different compositions andrepeating step (b) after one or more of the time intervals byintroducing a different one of the compositions onto the galvanizedsurface.
 9. A method of inhibiting corrosion in an industrial watersystem that is at least partially full of water and has one or moregalvanized metal surfaces, said method comprising: (a) adjusting thewater in the industrial water system to have a pH from about 6.5 toabout 8.2; (b) introducing an effective amount of a corrosion-inhibitingcomposition that includes one or more sulfide-based white rustcorrosion-inhibiting compounds into the water of the industrial watersystem when said system is either under load or not under load; (c)circulating the water of the industrial water system for a time intervalto contact the sulfide-based white rust corrosion-inhibiting compoundwith the galvanized metal surface to form a barrier on the galvanizedmetal surface, if the system was not under load; (d) operating thesystem for the time interval to contact the sulfide-based white rustcorrosion-inhibiting compound with the galvanized metal surface to formthe barrier on the galvanized metal surface, if the system was underload; (e) optionally overlaying the barrier by: i) unloading the system,readjusting the pH of the water in the system to be from about 6.5 toabout 8.2, reintroducing an effective amount of the corrosion-inhibitingcomposition into the water of said system, and circulating the water ofthe system, or ii) keeping the system under load, readjusting the pH ofthe water in the system to be from about 6.5 to about 8.2 andreintroducing an effective amount of the corrosion-inhibitingcomposition into the water of said system; and (f) operating theindustrial water system under load for one or more additional timeintervals and optionally repeating step (e) after one or more of theadditional time intervals.
 10. The method of claim 9, wherein theindustrial water system includes a cooling water circulation system. 11.The method of claim 9, including adjusting the pH of the water in theindustrial water system to be from about 6.8 to about 7.8.
 12. Themethod of claim 9, wherein the corrosion-inhibiting composition includesone or more polyalkoxy compounds.
 13. The method of claim 9, includingadding another composition including one or more polyalkoxy compounds tothe water of the industrial water system either simultaneously orsequentially with the corrosion-inhibiting composition.
 14. The methodof claim 9, wherein the corrosion-inhibiting composition includes fromabout 1 ppm to about 10,000 ppm of the sulfide-based white rustcorrosion-inhibiting compound.
 15. The method of claim 9, wherein thecorrosion-inhibiting composition includes one or more compounds selectedfrom the group consisting of: other corrosion inhibitors, scaleinhibitors, fluorescent tracers, and water treatment polymers.
 16. Themethod of claim 9, including adding one or more other corrosion or scaleinhibiting compositions that include one or more corrosion or scaleinhibiting compounds with or without one or more fluorescent tracercompounds either simultaneously or sequentially with thecorrosion-inhibiting composition.
 17. The method of claim 9, wherein thecorrosion-inhibiting composition includes one or more other corrosioninhibitors selected from the group consisting of: phosphates;phosphonates; phosphinates; silicates; molybdate; tungstate; borate;zinc and its salts; vanadate; chromate; polycarboxylates; andcombinations thereof.
 18. The method of claim 9, including adding one ormore water treatment polymers either simultaneously or sequentially withthe corrosion-inhibiting composition, said polymer selected from thegroup consisting of: polyacrylic acid; polymaleic acid; copolymers andterpolymers of acrylic acid, maleic acid, acrylamide, andacrylamidopropyl sulfonate; prism polymers; sulfonate-based polymers;and terpolymers or copolymers of acrylic acid, acrylamide, andsulfomethylated acrylamide.